Lpc2000

Thanks

--- In lpc2000@yahoogroups.com, "ebland_us" <ebland_us@y...> wrote:
> It sounds like your inputs aren't truly differential.  You've 
> referenced the V- input as a reference 90mV.... which makes it a 
> unipolar signal, essentially.  A differential input won't have 
this 
> type of reference as Karem mentioned below.   You could force the 
> inputs into the 0-5V range by using a 2.5V ADC reference.  You can 
> still you a differential input but will then want to make the 
input 
> amplifier's common mode reference at 2.5V... or half of the 
reference 
> voltage so that it's centered in the range.  
> Edwin
> 
> --- In lpc2000@yahoogroups.com, "Leighton Rowe" 
<leightonsrowe@y...> 
> wrote:
> > The analog inputs and references look stable to me. No floating 
> > pins. I've made the Vin- input closer to ground:
> > 
> > Analog input (always +ve)---> Vin+ 
> > 0V                       ---> Vin-
> > 3V                       ---> Vref
> > 5V                       ---> AVDD/DVDD
> > 
> > ...but the same readings are still coming out. Maybe it's 
because 
> > I'm using a "true differential" ADC. I heard the setup's 
different 
> > compared to pseudo differential which I'm more accustomed to 
using.
> > 
> > --- In lpc2000@yahoogroups.com, "Kerem Or" <k.or@s...> wrote:
> > > It appears there is a common mode voltage problem. Check if 
there 
> > is a 
> > > current return path between AIN-/AIN+ and AGND. What you 
observed 
> > can happen 
> > > if the signal source is floating with respect to AGND. As you 
> have 
> > noted the 
> > > AD accepts -2.5V to 2.5V. But since the part is not bipolar, 
the 
> > applied 
> > > input signal must not be above VCC or below ground with 
respect 
> to 
> > AGND. 
> > > i.e, -2.5V actually means 0V connected to AIN+ and 2.5V 
connected 
> > to AIN-. 
> > > It is not -2.5V with respect to AGND.
> > > 
> > > Just make sure voltage on any of the differential pins is in 
> > between the 
> > > part's common mode range.
> > > 
> > > Kerem